The present invention relates to technique for controlling a direct fuel injection spark ignition internal combustion engine.
Recently, the technique of direct cylinder injection in a spark ignition engine is under development to improve the fuel efficiency and emission control by Injecting fuel directly into a combustion chamber (or each combustion chamber). A control system for such a type normally effects combustion of a homogeneous air fuel mixture distributed uniformly throughout the combustion chamber by fuel injection on the intake stroke. In a predetermined engine operating region (such as a region of low speeds and low loads), the control system achieves ultra lean combustion by producing an ignitable stratified mixture closely around the spark plug by fuel injection on the compression stroke.
Japanese Patent Provisional (Kokai) Publications Nos. 62(1987)-191622 and 2(1990)-169834 disclose internal combustion engines of such a type. Japanese Patent Provisional (Kokal) Publications Nos. 8(1996)-296485 and 8(1996)-100638 further disclose related technology for activation of a catalytic converter.
The control system of the above-mentioned Japanese Patent Publication 8(1996)-296485 according to one interpretation is arranged to inject an additional amount of fuel into a combustion chamber during an open period of an exhaust port on the exhaust stroke so that much of the additional fuel is left unburned and supplied to the catalytic converter to promote combustion of the unburned fuel in the catalytic converter and to increase the temperature In the catalytic converter. However, this system presupposes the reaction of the unburned fuel on the catalyst, so that this system is not sufficiently effective in the state in which the catalyst is not active at all. Moreover, the reduction of time from a start of activation to complete activation entails deterioration of emission control performance (specifically HC emission to the atmosphere) during the control.
The control system of the above-mentioned Japanese Patent Publication 8(1996)-100638 is arranged to inject additional fuel into the combustion chamber on the early stage or intermediate stage of the expansion stroke. By flame propagation, the additional fuel is ignited and burned to increase the exhaust gas temperature. By increasing the exhaust gas temperature, this system can increase the temperature of the catalytic converter irrespective of whether the catalytic converter is activated or not. However, when the temperature in the combustion chamber is too low to promote vaporization of liquid fuel as in a period immediately after a start of the engine, part of the additional fuel is likely to be left unburned and emitted to the atmosphere.
{Japanese Patent Provisional (Kokai) Publication No. 10(1998)-169488 (published on Jun. 23, 1998) shows earlier (non prior art) technology for increasing the exhaust temperature.}
It is an object of the present invention to provide system and process for promoting activation of a catalytic emission control device for exhaust gas purification, and reducing HC emission during the activation.
According to the present invention, an engine system comprises a direct injection spark Ignition internal combustion engine, and an engine controller.
The engine comprises a fuel injector for injecting fuel directly into a combustion chamber of the engine, and a spark plug for igniting an air fuel mixture in the combustion chamber.
The engine controller operates the engine in a first stratified charge combustion mode for producing a substantially stoichiometric air fuel mixture concentrated around the spark plug at a time of ignition in a predetermined engine operating region by controlling fuel injection quantity and timing of fuel injection during a compression stroke by the fuel injector and ignition timing of the spark plug. Furthermore, the engine controller detects a predetermined request condition requesting a temperature increase of a catalytic emission control device disposed in an exhaust passage of the engine, and operates the engine in a second stratified charge combustion mode for producing a richer-than-stoichiometric air fuel mixture of a rich air fuel ratio richer than a stoichiometric ratio concentrated around the spark plug at the time of ignition by controlling the fuel injection quantity and fuel injection timing of compression stroke fuel injection on the compression stroke by the fuel injector and the ignition timing of the spark plug when the predetermined request condition is detected.
According to the present invention, an engine control process for controlling a direct injection spark ignition internal combustion engine which comprises a fuel injector for injecting fuel directly into a combustion chamber of the engine, and a spark plug for igniting an air fuel mixture in the combustion chamber, comprises: operating the engine in a first stratified charge combustion mode for producing an substantially stoichiometric air fuel mixture concentrated around the spark plug at a time of Ignition in a predetermined engine operating region by controlling fuel injection quantity and timing of fuel Injection during a compression stroke by the fuel injector and ignition timing of the spark plug; detecting a predetermined request condition requesting a temperature increase of a catalytic emission control device disposed in an exhaust passage of the engine; and operating the engine in a second stratified charge combustion mode for producing a richer-than-stoichiometric air fuel mixture of a rich air fuel ratio richer than a stoichiometric ratio concentrated around the spark plug at the time of ignition by controlling the fuel injection quantity and fuel injection timing of compression stroke fuel injection on the compression stroke by the fuel injector and the ignition timing of the spark plug when the predetermined request condition is detected.